There is an increased incorporation of radioactive uridine into RNA isolated from nuclei and from the ribosome pellet of the brains of mice conditioned for 15 minutes to avoid a shock. The increases are not observed in liver or kidney, and they are not general throughout the brain, but are restricted to the limbic system. There is also an increased incorporation into polysomes. The increased radioactivity in polysomes is not a consequence of non-specific stimuli. The physiological significance of the increase of radioactivity in polysomes is not clear, but it might be related to maintenance and replenishment of cellular constituents, or to biosynthesis of new constituents of a neuron as it becomes involved in new synaptic networks in which memory may be encoded. The proposed research is an attempt to further elucidate the significance of this phenomenon. Because of the known effects of hormones on RNA synthesis in other tissues, we want to elucidate hormonal influences, if any. We also want to determine whether the increased incorporation of uridine into RNA and polysomes is related to consolidation processes by monitoring this incorporation when consolidation is started again after it has been stopped by ECS or by cycloheximide. We would also like to examine the effect of various agents that affect memory consolidation on RNA and protein synthesis in the brain and to ascertain whether there is increased incorporation into brain protein of the trained mouse. Finally, we wish to study the effects of other physiological and biochemical changes thought to be associated with increased RNA synthesis in animals.